A reference datum is a known and constant surface which can be used to describe the location of unknown points. On Earth, the normal reference datum is sea level. On other planets, such as the Moon or Mars, the datum is the average radius of the planet.

You are publishing a tiled map service using the ArcGIS Online/Google Maps/Bing Maps tiling scheme and there is no datumtransformation from your data frame's datum to WGS 1984 Major Auxiliary Sphere.

Datum: A reference location or elevation which is used as a starting point for subsequent measurements. Sea level is a datum for elevation measurements.

DATUMS4-1. The earth is an ellipsoid, not a sphere, flattened slightly at the poles and bulging somewhat at the equator. Datums are reference surfaces that consider the curvature of the earth for the mathematical reduction of geodetic and cartographic data.GEOID ...

Datum, Spheroids and EllipsoidsUnlike local surveys, which treat the Earth as a plane, the precise determination of the latitude and longitude of points over a broad area must take into account the actual shape of the Earth.

DatumsA datum is a starting point for locating features on the Earth's surface; it is the origin point of a coordinate system. It defines the position of the ellipsoid (or spheroid) relative to the Earth's center. There are many different datums and hence many different starting positions.

A datum is a system which allows the location of latitudes and longitudes (and heights) to be identified onto the surface of the Earth - ie onto the surface of a 'round' object.The basic mathematical/geometric principle which is used is that: ...

Datumtransformations using Molodensky equations (implemented in most geo-software) are becoming increasingly important, because of the growing use of GPS data.

Datumconversions are automatically handled by the PROJ.4 library if "+datum" setings are specified on both the input and output projections on the command line. The "+towgs84" parameter can be used to define either 3 or 7 term datumtransform coefficients, satisfying this requirement.

DatumPoint, line or surface used as a reference for a measurement of another quantity. Point, line, or surface used as a reference (i.e., surveying, mapping, or geology). Combination of parameters and control points used to accurately define the three dimensional shape of the Earth (spheroid).

DatumA reference point or surface against which position measurements are made, and an associated model of the shape of the earth for computing positions.

Geodetic DatumThese materials were developed by Peter H. Dana, Department of Geography, University of Texas at Austin, 1995. These materials may be used for study, research, and education in not-for-profit applications. If you link to or cite these materials, please credit the author, Peter H.

Multiple datum LRS and color coding of complex infrastructureobjects often result in misleading or incorrect computation, identified by Sutton (1996) as network pathologies.

Changing datums (for example, from NAD 27 to NAD 83) can be difficult or cumbersome.Projections are usually implemented using power series approximations that might be inadequate for high precision work.

Geocentric datum relate coordinates to the earth's center of mass. Such datum have been improved by modern satellite data. The North American Datum of 1983 is based on the modern GRS 1980 ellipsoid - almost identical to the most widely used WGS 1984 ellipsoid which is also geocentric.

Typically consists of a projection or a system of projection zones plus a geodetic datum and ellipsoid. NDVI p. 220 difference between two bands (near infrared minus visible red) divided by the sum of the two bands; high values indicate active vegetation growth; often applied to NOAAAVHRR data.

BenchmarkA brass or bronze disk set in a concrete base or other permanent structure, inscribed with a mark showing its elevation above or below an adopted vertical datum.DatumIn geomatics, a mathematical model used to approximate the size and shape of the earth.

An estimate of the earth's surface based on an ellipsoid provides a determination of the elevation of every point on the earth's surface, including sea level, and is often called a datum. Over time, and in different countries, many datums have been developed and used.

A digital representation of a continuous variable over a two-dimensional surface by a regular array of z values referenced to a common datum. Digital elevation models are typically used to represent terrain relief. This is a common GIS product created at a variety of scales.

There is another critical bit of information that is required before you are totally confused: the datum. The need for a datum is the consequence of man's inability to describe mathematically the exact shape of the earth.

Z-score The (signed) number of standard deviations an observation or datum is above or below the mean. A positive standard score represents a datum above the mean, while a negative standard score represents a datum below the mean.

Both 32661 and 4326 use the WGS 84 datum and ellipsoid but one is long lat (4326) and one is a meter based one. The WGS 84 simply defines the ellipse and datum.

But the earth's mountains bump-up and valleys bump-down from the ellipsoid so a datum is designed to fit the earth's surface that accounts for the actual wrinkling of the globe as established by orbiting satellites.

Take a look at the projection definition you copied (Imported) for the la_to_ny shapefile you created with ArcToolbox, what Spheroid was used with the Datum?3b. Briefly state what the difference between Spheroid and Datum is.3c.

With names like State Plane, UTM, Albers and many others, projections can be quite thorny for novice GIS users (compounded by a related factor, called a 'datum' which defines the surface of the earth as of a certain date).